Method for preventing channeling in hydraulic fracturing of oil wells



DCC. 15, C. E. CARR METHOD FOR PREVENTING CHANNELING IN HYDRAULICF'RACTURING OF OIL WELLS Filed OCT'. 14, 1960 2 Sheets-Sheet l 7 R /W/mwe E NA N V2 N HHHUJ.. 1E m -,hn............... W M w W Dec. l5, 1964 ECARR 3,161,235

C, METHOD FOR PREVENTING CHANNELING IN HYDRAULIC FRACTURING OF OIL WELLSFiled Oct. 14. 1960 2 Sheets-Sheet 2 Ff FT {Sg-V22 IVENTOR. CHQEES. f.096@ United States Patent Office 3,161,235 Patented ec. 15, 19643,16L235 METHOD FR PREVEN'E'NG CHANNELNG IN HYDRAULEC FRACTURNG OF @ELWELS Charies E. Carr, RO. Box 419, Lawrenceviile, Ill. Fiied Oct. 14,3.96%, Ser. No. 62,767 i8 Claims. (Cl. 16e-29) The present inventionrelates to a method for treating producing formations. The methodcontemplates the treatment of geological formations. While suchtreatmeut is normally of oil-bearing formations, treatment of water, gasand other formations may be accomplished. More specifically, the methodrelates to confining to a selected stratum or strata the materialsemployed in the treatment of such formations. One of the most importantcommercial advantages achieved by practicing the present invention is inthe prevention of channeling or failure of bond between thecasing-cement-formation relationship from occurring during pressuretreatment of a geological formation.

This application is a continuation-in-part of application 37,769 filed Iune 21, 1960, now abandoned.

It is well known to promote oil production from oilbearing formation byfracturing or acidizng the same. The fractures in the formation createdrainage channels for the oil. T le acid similarly creates drainagechannels by dissolving soluble relatively impermeable materials. Infracturing operations, the well casing and surrounding cement, if therebe any, is perforated adjacent the zone to be treated; an interval inthe well adjacent the zone is isolated by appropriately spaced packers;and pressurized fluid-normally an oil or emulsionis pumped into theisolated interval from whence it ows through the perforation and outinto the formation where the pressure opens various drainage channels inthe formation. Pressurized fluids are also employed in related processessuch as acid treatment and the like. Oftentirnes a sequence ofpressurizing steps is employed.

The pressurizing is most effective in fracturing when the hydraulicfluid is directed into and confined or maintained in the formation to befractured. Additionally, an advantageous economy of fracturing orhydraulic fluid is effected when such confinement is obtained.Unfortunately, faults are often present in the well structure and thesurrounding formation that operate to cause channeling and/ or drainingoff of the fluid. Worse, many of these faults direct the fluid intowater-containing formations and result in admitting water into theoilbearing formation, or into the well directly.

In this connection, a serious type of fault leading to waterdisplacement and loss of fracturing fluid results from defective bondingor sealing between the casing and the well cement surrounding it, orbetween the well cement and the formation, or a combination of the two.Such faults can be particularly serious because, for example, thepressure drop is comparatively low for a ow path from the perforationalong the casing or cement through the fault, thus leading to anunproductive well requiring extensive further treatment. Correctivemeasures are oftentimes difficult in that the fracturing operation isalready completed before detecting the failure.

Broadly, the invention contemplates establishing in or adjacent to theoil-producing formation to be treated an annular' sealing cavityadjacent the casing spaced from the location where treatment is to beintroduced into the formation. The materials used are compatible withconventional treating materials. One example of the invention follows:The sealing cavity is established by severing the casing and cement andforming a cavity in the formation, all below the fracturing fiuid zoneof entrance; and filling the casing with a plugging agent to form a bedhaving an upper level between the sealing cavity and the zone ofentrance. The necessary zone of entrance is prepared by suitablyperforating the casing and by seating a packer or packers at suitablelevels above the zone of entrance. lt is preferred tocompletely severthe casing and cement at the sealing region, i.e. a 360 circular arcdefines the cut made. It is also possible to perforate the casing,however, while completely severing the cement. When the treating fluidis applied under pressure to the zone of entrance, the plugging agentfills the annular sealing cavity. Pressuring is then applied, and thelevel of the plugging agent checked, to insure that the annular seal iscompletely effected. The hydraulic and/ or hydrostatic pressure is alsoutilized to maintain the seal. Variations in the sequence of steps arepossible, all to the end of establishing a sealing region that opposesor blocks iiow through faults that occur exterior to the casing. Also,the invention is not limited to the type of plugging agent used, butincludes any material owable into confining or sealing relation with theformation responsive to pressure.

Occasionally some geological formations will have a stratum containingWater or salt water that lies immedi ately above the oil-bearing zone.Such formations are found in Kansas. The present invention includesestablishing a seal to prevent channeling of treating fluid into theupper one of these zones into the oil-bearing zone and ultimately intothe well. The treatment is advantageously employed where a fault in thecasing-cement-well bore joint would connect the oil-bearing zone withits overlying water-containing zone.

One manner of establishing a seal is discussed above. Another manner ofestablishing a seal for such an overlying stratum is to provide a liquidbody in the Well casing itself and then to establish a mass of sealingmaterial floating on top of the liquid. The liquid level .is adjusted sothat the sealing material is positioned adjacent a cut made through thecasing and into the surrounding formation sealing cavity, and above thelocation where `treating material is to be introduced into theformation. By seating a packer to seal off the well bore above thefioating mass and then applying fracturing pressure from below thefloating mass, it is possible to dnive a portion of the floating massthrough the cut and into the sealing Icavity and thereby establish aseal. The seal is advantageously maintained during fracturing and othertreating operations by the pressure within the well casing urging thefloating body out into sealing contact with the formation.

One object of the present invention is to provide a method forcombatting pressure treatment problems arising from faults incasing-to-cement bonding and/or in cement-to-formation bonding. Anotherobject is to provide a method of preparing the well for subsequentexecution of a fracturing or acidizing operation. A fuuther object is toprovide a method of preparing the well and executing a treatingoperation whereby flow or channeling (through faulty bonds of the naturedescribed) of the treating fluid is opposed, thereby maximizing thetreatment obtained for the materials and energy applied.

One feature common to many of the previously known corrective techniquesis that the action to be taken occurs after the problem arises, at atime when it is not convenient to take such action and after loss ofiiuid, Water displacement, and related injuries have been suffered.

A feature of the present invention is that prophylactic action can betaken beforehand.

Other objects, advantages and features will become apparent from thefollowing description and the drawing wherein:

FIGURE 1 schematically represents a cased well with a tool thereinsevering the casing and well cement at a depth below that proposed forinitiating fractures in an oil-bearing formation.

FIGURE 2 schematically represents a cased well undergoing perforation at`the proposed fracture initiation depth and after completion of theoperation of FG- URE 1- @FIGURE 3fsc`hematical1y represents a cased Wellwith afbottom packer and fsandplug emplaced. l -FIGURE 4shema'tic'allyrepresentsa cased well after hekopera'tin f FIGURE 3 whereintheintervalto be treatedfisiisolated withan upper .packer during or-aiter kthe ,application of 'fracturing pressure.

l. i GURE 5 schematically Vrepresents an alternative ftec'hrlique'forYopening the wellca'sing at the respective depths Y ofracturingandsealing. v

FIGURE'6 is a'sc'hematic representationl of a' horizontal ySectionAtaken along line 6 "6 O"FIGURE 2.

yFIGURE7 isa-'schematic representation of a horizontal vsec'tionftakenalong line '7-'7- of'FGURE.

FIGURE `8 "is la schematic representation of a well cross sectionYillustratingone manner of carrying out the present invention. n

'FIGURE /9 is a schematic'well cross"section'illustratingvanother.i'na'ri'nerA of practicin'gthe invention.

`FGURE`1`0is aschematic 'wellrcross section of a modication of FIGURES.,*Y The'inventio'n is carried out withthe' use of conventional tlsin anexisting cased well. The `drawings illustrate varius'stages'in'theprocessor preparing a'w'ell'in ac-` cordancewth the invention.

fRfe'ring now toFIGURES 1 through 7, and toFlG- A.

'URES`1 andf6 in particular, al cased well borel is shown asfeiiteridingtlirougha 'plurality of geological strata repre-Y Vfsentative oftheVearths Vstr't'lcture in oil-containing areas. "It is'to'beY understoodthat the .geological structure shown is representative only and isemployed `for theipurpose '/ofieipla'ining the inventionyrather thanlimiting the inl ve'tionfs'tr-ictly'to A"treat-Intent ofthe identical*geologicall structure. -In the drawing, thevarious strata from lthe topdown, as shown, are: Alirnestone 12,211 oil sandlii, v

''An4 oir-bearmg'formation 'such as the on sind; 141s 'selectedasthe'lzone to betreated. It'will be appreciated, however, "that j'glasand 'water 'formations )may also be `s`o-treated. `Then, atleast oneldepth, 7J-7 is selected "as' that where'the' treatinguid is to beintroduced -intol the formation at a desired 'zoneof entrance.

Following the Y 4 l A. Boynton, the U.S. Patent No. 2,302,567 issuedNovember 17, 1942 to F. E. ONeill, and is further described in the June15, 1959 and May 9, 1960 issues of the Oil and Gas Journal in thearticles beginning on pages 68 and 127, respectively. The abrasivestream is led to the tool 3i) through the tubing string 32 whichfisrinturn connected at the earths surface to a suitable .pump yandsupply'source for ythe 'cutting uid (not shown). As the stream ofcutting fluid 36 emerges from 'each nozzle 35 o r the tool 3), itimpinges against the 'casingt abrades the, same Vand removes it, andthen Vcontinues to abrade the Well cernent 22 and'finally beginsto-abrade-the oil sand oradjacent formationlfi to ultimately form a sandseal cavity denoted as `38. ,By lrotating the tubing 32, the toolf) cutsthroughout a 360 arc thereby/severingthe casing and cement. Thesealing'"cavity per seis annular with Yrespect tothe region formerly occupied'bythe removed 'portionsof the casing and cement, as seen in FGURE 6.

Other cutting means can be employed. For example, .an ,expandable millorcutting bit'could be lowered to 't5-T6 and rotated untilY an appropriate.cuthad been'made through the casing, cementfand into the oil sand.Alternatively, it is possible to use an Oxy-acetylene cutting Vllameto'cut through both the steel 'and the concrete. Other'types of cuttingllames are alsocapable of' employment. The 19'60`OilandGas Journal,supra,fde scribesva'rious'llame-cutting and other procedures which areadaptable for employmenthere. Also, various'per- 'foratingtechniques areavailable tto-accomplish the necessarycut. Y

Inthe lordinaryoperation, it is preferred to completely 'severthecasingZl and vcement`22 throughout a 360 circular'arc. vIn'thisfashion, provisionfis made for an annular sealing' cavity 3810 receiveand provide an annular' seal in the manner described below. In unusualsituations, it may be desiredto'only severa portion of the asin'ga'ndthecement. Complete severance yor cutting A"throughout"360 is btainedby theprovision of a plurality of streams 36, or by'rotatingl the cutting tool'36, 'or 'by 'a' combination of' theftwo. 1

AkRefer'ririg'nowV to FGURE 2, the tool '301s n'eX-t moved vup to thewell-to the '7`-7'leve1 and suspended there by the tubing andcentralizer inV anl appropriate position. A'trea'ting cavity or zone ofVentrance '40 isprepared by againfdirecting a stream "360i cuttingparticles against 'the Vcasir'igfthe cement, andl finally' into theproducing kffor'mation"14. Thisprocess isgenerally similar'rtotnatestablishment of`7-"7, adepth orlevelbeneath'that, but

"s'till"in"tles`ame oil sandv or producing 'formation 14 isfselec'ted.f'1`he 'latter depth kis denoted as 6-6 and is Vthe depthatWhi'ch'the sealing cavity is formed to form fthe seal or'mea'ns'for'conning'in accordance withthe "presenfinve'ntion Followingthexselecti'ons of 7 7 and 6-6," a cutting Y ,tool y3.0 run down throughthe casingfto vthe level of "646s Th'etoo1`30'is ordinarily suspended atthe bot- .tornotfa .string ofvtubingor'drillpipe 32. AdditionalVsupport' to Vaidincentrally vdisposing the toolrtl,A is der'ived' froma-'centralizer V34 which is attached to the ytubing 32. MForthe purposeof this description, itis assumed` ."'thi'at conventional ldrilling'equipment and accessories therefor VVisfpiot'fided. Such equipment isdescribed in Pef trl'eumProductionEngineering (4th ed.), by `Lester C.

for "forming the' sealing cavity 38.

y"It'.is'jpreferredto form ,a tre'atingj cavity vor-z'one of entrance'bycomplete severance in afas'hion similar to that 10h38.. "Howevelg'insome instances there is great danger tiratthe'intermediate section yofcasing and cement '42 may slip and -fall down into the sealingcavity`3S, thereby "to 'block the' sameV from'iuture oper-ations. y lnsuch in- Astancfesyit ispre'ferred not vto make ya complete 360 cut,

but -insteadto'thold theV tool 30- still and to perfor-ate themaybed'esirable and it is certainly an alternative,'to`pre meanslforemitting. a streamof abrasive particles carriedv *pare the .cavitiesSSV-and '40 `inreverse of the order just given. i l

Referring now/to FIGUREv 3, vthenext sequence of `ste-psinvolvesrplacing a pIugorInidge 44 atsome point inthe casingbeneath 66.- 1 It` is preferred that the plug be drillab-le so that it can kberemoved to provide access .to regionscf lgreater depth. Accordingly, a.drillable vvassembly'rsu'ch.as that described on pages 475-477 of 55Uren, supra, may be employed. Of course, other drillable bridgingassemblies can be used. In using an apparatus such as described by Uren,it is contemplated that the bridge will be completely sea-led with nothrough passages when seated in the well and therefore the appropriatesealing means can be inserted in the plug prior to its insertion in thewell.

The bridge 44 is run into place by attaching it to the end of the tubing32, lowering it to the proper depth, and then exerting a suliicientpressure of water or the like to cause the slips (not shown) to engagethe casing in a positive mechanical manner. After the bridge 44 isseated, the tubing or drill stem 32 is disconnected therefrom and movedupwardly to approximately the position shown in FIGURE 3. Then apumpable slurry of sand and oil, or sand, cement and water or othersuitable material is pumped down through the drill stem until the casingZ above the bridge 44 is filled with the plugging agent to a levelintermediate to cavities 38 and 40, i.e. to a level along theintermediate casing in cement section 42. If desired, sand can be mixedwith petroleum or some hydro-carbon derivative in order to provide thepum-pable slurry.

It is important that the treatment not be performed until the depth ofthe plugging agent is accurately determined and maintained at `a pointimmediately below the cavity 7 7 and above the cavity 6 6. This may bedone by mechanically sampling the top level of the plugging agent, thistechnique being more commonly known as thiefing Thereafter the treatingfluid is pressured into the drill stem 32 and pumped under pressure downthrough the well, through the passage 48 and finally out through thezone of entrance to the fracturing cavity dil into the formation 14.

Treatment may also be accomplished with the drill stem 32 removed fromthe well, and the fluid injected directly down the casing string.

Great pressure is exerted on the formation in fracturing. A consequenceof `applying the pressure of the fluid, which is preferably an oil, `anoil-water emulsion, o1' the like, is to cause fractures in the oil sand14- which in turn constitute drain channels, denoted herein as thecracks 50. These cracks appear in random Afashion according to thenature of the oil sand or other oil-bearing formation i4. At the sametime that pressure is being applied to fracture the formation, the samepressure urges the plug 46 into place and causes a flow of the pluggingmaterial out and into the plugging cavity 38. Thus, as long as treatingand hydro-static pressure exceeds the formation pressure, there is aforce that urges the plug i6 out into sealing or confining engagementwith the formation in the annular cavity 38. This urging is constant andcontinuous during the application of pressure and provides the annularseal as best seen in FIGURE 6. This annular seal opposes the liow offracturing or treating uid down through channels that may be present dueto faults in the cement casing or formation to cement bond. Standardcompletion procedures and techniques are then employed.

FIGURE 5 shows an alternative technique for creating the two cavities 38and 40. The process of FIGURE 5 involves the use of a tool a which isgenerally similar to the tool 3) of FIGURES l-4. However, the tool 30ahas groups of nozzles vertically spaced apart, each group of nozzlesbeing located at the proper level 6 or 7 when the tubing or drill stem32 is properly positioned within the well. When the abrasive fluid ispumped out through the nozzles, the two cavities are formed generallysimultaneously. The apparatus in FIGURE 5 is most conveniently used whenit is desired to have both the fracturing and the sealing cavities 38and dit) of like conformation, that is, to have them both eithercompletely annular which is obtained by rotating the tool 30a within thecasing, or where it is desired to have only a perforation in the casingin which .case the tool 30a is held still.

E A similar arrangement could conveniently be used with a cutting liame.

A wide variety of materials are suitable for use as a plugging agent infilling up the annular sealing cavity. Included in the term pluggingagent are: A gel, preferably one that can be formed in situ and which isstable but can be broken by contacting with a suitable gelbrealrer orsolvent; particulate materials such as sand, cellophane in divided form,cottonseed hulls, wood fibre, ground corn cobs, a combination of any ofthe same, and on occasion cementit-ious materials admixed with one or acombination of the same; and where nondissolvable soli-ds such as someof those listed as particulate materials are used, it is preferred thatthe plugging agent include a suitable iiuid vehicle for carrying thesame down to the appropriate place in the well. When the term pluggingagent is used below, it is intended to include materials such as thosegenerally described in the preceding listing, but not limited thereto.Further, when the term particulate material or the like is employedbelow, it is intended to refer to such items as sand, etc. as citedabove, but without a limitation to only those materials recited in thelisting. It is preferable that the plugging agent (which includesparticulate materials) be of such a fluid-like nature that it may beflowed into confining relation with the formation whereby the fiow orchanneling of fluids is prevented past the seal that is accomplished -byinstalling the plugging agent in the annular or sealing cavity.

It is epreferred that the invention be applied to the treatment ofoil-bearing formations by such means as fracturing, acidizing and thelike wherein fluids are utilized that may channel into the wrong place.However, other types of formations, including those containing gas orwater (ordinarily salt water as found in association with petroleumminerals) can also be treated. Treatment of waterbearing formations issometimes desired in order to provide fluid for use in water floodingoperations, the preparation of drilling mud, and the like.

The method has been described with reference to a preferred embodimentwherein the annular plug is installed at a position beneath that wherethe perforation into the formation is accomplished. It is alsopracticable to emplace the seal above the zone of treatment, c g. wherethere may be a iiuid contained in the formation that would interferewith either the treating process contemplated or with subsequentproducing operations from the formation once it has been treated. It isfurther contemplated in this connection that seals be emplaced above andbelow the zone that is to be treated by the various means rdescribedherein.

Where the seal is placed above the treated zone, it is ordinarilypreferred to pressurize it into confining relation with that `formationbeing treated. One way of accomplishing this is to isolate the seal byseating a packer above the bed of plugging agent, then to fill the zoneabove the isolated seal with fluid, and then to pressurize both the sealzone and the treated zone.

FIGURES 8, 9 and l0 show procedures for establishing a seal above thetreated zone. In these figures a floating plugging agent is used. Thelevel of the plugging agent is obtained by seating a packer and suitablesealing means above the floating mass. The sealing effect is obtained bythe pressure applied in treating the formations as by fracturing,acidizing, and the like.

Referring now to FIGURE 8, there is shown a well cross section having anoil-bearing zone 14 that is to be treated by fracturing through thefracturing cavity 40. Overlying the zone 14 is a stratum 11 whichcontains water or salt water and which it is desired to seal off byestablishing an upper sealing cavity 60. The perforation of the casingZtl, the cement 22 and the stratum 11 is preferably obtained in thefashion set forth above for the lower sealing cavity 38 and thefracturing cavity 40. A complete annular cut presenting a cross sectionas in FIG- URE 6. is preferred; but; a, cross section such -asyshown inFIGURE 7, can be employed where structural reasons v demand it.

When the sealing cavity V6 0`has been prepared, a plug.

, plug 46 is emplaced.

Most well casings Iare filled with fluid during such operations,forexample, fracturing uid, water, or the like. As-v suming such toV bethe case, a large amount of floating malfo on which they loat. 'Thedifference inV specific Vgravity should be as large as possible Yand canbe obtained both by increasing the gravity of the* liquid by theaddition of*A chemicals, etc., by the selection of the rnaterials tocomprise the ybody 62,` and even by coatingthe materials in the( bodyvvith'aV waterproofing salt such as aluminum acetate where water is theprincipal solvent in the fracturing `fluid, or by coating thervmaterials with some other suitable solvent-,resisting'material to theend that absorption of the liquid by Ythe'solidrs making up thefloatingbody will be reduced and thereby maintain the tloat-y floats on topofrsuch luid. The quantity of the floating material is 'suicient thatitills theinterval denoted -as 64 int FIGURE 8 when the body ofvmaterialis ultimately positioned. The interval Gti-extends downwardly fromapacker assembly to a point intermediate the upper, sealing cavity 60 andthe fracturing cavity 40. The tubing string is thenassembled andincludes a packer or bridge assembly 66 having selectivelycontrollableslips 68which can be jammed into engagement with the casingl and withdrawn from such engagement upon suitable manipulation by theoperator. Immediately below the packer assembly is positionedfa one-wayseal cup 70.` Artail pipev` of tubing`72 depends below the assembly ofelementsA 66, 68, 7 0 and is long enough to extend completely throughthe body of floating materlalfinto the liquid below.

When the tubing string 32 has been assembled to include elements 66 68,70 and 72.it is thenpositionedvin the casing Ztiand started down,through the well.y As this assembly is moved down-1 through the well,the'llquid within the casing enters the tail pipe '-72 and runs upability of the materials yin thejbody 62. The liquid is any well-knownfracturingfluid such as 'emulsions of acid land petroleum fractions orof the latter vwith water; crude oil; napalm gelsand Ithe like. Y Y .4 ly i A FIGURE 9 illustratestamodification ofv tbe-embodiment of FIGURE 8wherein sealing cavities at theupper andk lower portions of aninterval-are ysealed at about the same time. To accomplish this,ar'liquid vehicle is admixed with a plugging agent that willzoat onVtop'of the liquid or iluidderived therefrom and a plugging agent thatwill sink inthe liquid ora iluidrderived therefrom. kThe mixture isVthen introduced intouthe interval to be sealed. (The respectiveplugging agents are freedfrom entrainment by such techniques asbreakin'gargel by contacting it for a time with a.gelbreaker if theliquid vehicleis a gel, allowing theliquid vehicle to change visthroughYthe tubingv32.V lf desired, the packer 66 can ,have Y, suitable `bypassvalves constructed within it so that the .liquid is merely transmittedfrom underneathjthe assembly of elements 6,6-72 to above such assemblyYof ele,-V ments. TheA particles and materials making up theiloat` .ingbody ofmaterial 462 cannot get into the tail pipeV7-2 becausethey float.on tQp ,0f the liquidrand willvnct citicalate around the bottom ofthetailA pipeas long as the latter is long ienough to depend in'to theVliquid supporting the'qatingbodyez. l

the casingztl. Thereupon the fracturing operation can -Eracturing iluidiswpumped. down through commence.

cosity merely by 'the lapse of time, and inl some instances, by dilutingthe liquid vehicle to a lower` viscosity by adding a solvent. Theparticular liquid-which term is herel used `to include liquidcompositions and` mixtures, gels, emulsions-and the like-isselected'raccordingto the type of formation and the character oftreatment to be given the formation.. The'types of liquids arewell-known to the prior art and thecomposition of the liquid vehicle perse constitutes no' part of the present invention.y However,

'the' use to which sucltV liquid is put in acting as a vehicle for'theplugging agent(s) is part `of the present invention.

lf ltheformation tobe treated isa limestone or dolo- Vmite, it is highlydesirable to acidize the same as part of the fracturing opera-tion, Theliquid vehicle selected for practlcing'the invention OFIGURE 9accordingly will include 'aV suitable acid. The liquid Avehicletispreferably ani acid-kerosene.emulsion. One such emulsion is taught inthe September 1953 issue of the Petroleum Engineer in the article onpages B-l4 through B-lS. Hydrochloric acid, a co-minercialgrade ofkerosene, a corrosion inhibithe tubing 32 and out of the tail pipe 72,through .the frac;y

'- Aturing cavityV 4t/9 and into fracturing contact with the '14; Thepressure loftheifracturing Vfluid isV formation such'tha ltnrges theHeating material ,62 vout into sealing engagement' v vith the cementVand formation. They pres-v sure of the fracturing iiuidmaintains thisseal. The iioat-V ing material is, of, course, pressure responsive tothe extent that it owsjnto sealing engagement with the .cement andVformation in response to the fracturing pressure. Where thecircumstances .call torit, thetubing and tail :pipe may haveconeentrictubes .mounted therein. and/ or packer 6 6f ymay have` a lay-pass valveunit therein so that liquidsori'ginally in the well ycasingcan bedisplaced from the fracturing region by the, fracturing uid prior to thetime that fracturing is commenced. l

Suitable materials for thebodyofiiloating'material include: 1Chopped `oriinely divided expanded cellular polytor to protect the casing and othermetal parts from the f acid, an Vemulsitying agent, and a'de-emulsifyingagent are all mixed together.l Such-an emulsionis time-breaking. Thatis, the emulsion'is quite thick butlwill break j downand yield a liquidof much less vviscosity after a predetermined length of time; Thevamount of time inproximatelytha't of kerosene.

lvolved, variesin accordance with thedown-hole temperature.The'consistency after ythe emulsion breaks isfap- Using aliquirdv'vehicle comprising the acidl-ierosene emulsion describedabove,sand and Styrofoam (the styrene `suchassold under they trade marklStyrofoam and manufactured by the, Dowy Chem'icalCompany of f-choppedyor nelydivided corkgrsawdust; and those mate-r rials listedabove as being a pluggingagent, whenever si@ materiels. ,are @tlowepspeiesravty than the liquid latterin finely-divided form) are addedtothe vehicle and introduced intovan interval of the'bore hole that hasbeenisolated by ,packers seated kabc-ve and below the respectiveupperandlower sealing cavities. When the interval lis completely filled Awiththe mixture of emulsion Aand plugging agents, itis .allowed toremain atrest for somel predetermined vlengtlr of time atthe endfof which theemulsion will'have' broken, the sand .will have sunk to the bottom ofthe interval to Ia'position adjacent the lower sealing cavity, and thevfStyrofoa-m will have risen `to the topof the liquid to la positionadjacent thc'upper sealing ,cavityr ofthe interval; '.Fracturingopera-tions lare now commenced in the usual manner, the hydraulic'pres-Grdinarily, it would bei preferred to introduce additional aie-1,235

Vquantities of the emulsion so that it can flow out into the formationthrough the fracturing cavity.

In the embodiment of FIGURE 9, the packer assembly 66 does include aby-pass passage 74 and a by-pass valve 75 for controlling fluid flowthrough the passage. Alternatively, concentric pipes with suitable checkvalving therein may be employed in the tubing string 32. The packer 66is positioned in the well and the liquid vehicle plus plugging agent(floating and sinking) is introduced as by pumping down through the tube32 into the region below the packer assembly 66. The by-pass valve 75'is open during this time so that other fluids are displaced from thisregion. When the displacement has been completed, the valve 75 is closedand the gel is continued to be forced into the region between the lowerplug 44 and the packer until such time as the entire region has beenfilled with the mixture. Catalyst for breaking the gel is frequentlymixed with the liquid vehicle if the latter is a gel. When the catalystoperates, the vehicle changes viscosity which falls to the bottomforming the sand plug 46, and the floating particles which then rise tothe top of the system where they congregate to form a floating body ofmaterial 62.

The pressuring operation commences, the various materials comprising thesealing plugs for the sealing cavities are urged into place and thefracturing fluid, preferably including a gel-breaker or being atime-breaking gel or emulsion, through pipe 32 from whence it flows outthrough the cavity 40 into the formation 14.

Various techniques may be employed for determining the location of thefloating bed in the well. One is by keeping a careful log of the well sothe position of the various sealing cavities and fracture cavities areknown. Using such a log, and knowing the amo-unt of space a particularamount of sealing material will take up in the well casing, appropriatevolumes of plugging agents can be introduced into the well casing.Alternatively, radioactive particles can be admixed with the variousplugging agents and the radiation level measured within the well todetermine exactly where the plugging agent is and to what level itextends.

The packer assembly 66 with its attendant seal cups 70 should bedisposed approximately two feet above the intended zone of fracture,i.e. two feet above the upper side of the oil-bearing stratum 14. Theupper sealing cavity 60 is disposed at an appropriate point between thefracturing cavity 40 and the position of the packer assembly 66. ln mostcases the upper sealing cavity will be located quite close to theboundary between the stratum i4 and the stratum ll.. In some cases itmay be necessary to place the upper sealing cavity iin the oil-bearingstratum 14,. In other instances, as illustrated in FIG- URES 8 and 9,the situation may require the upper sealing cavity to be located in theupper of the various strata under discussion. The tail pipe 72 shouldextend to some place below the boundary of the floating body andpreferably should be somewhere between the lower bottom of the floatingbody 62'; and the sand plug 46.

FIGURE l0, which is an alternative embodiment of the invention shown inFIGURE 9, shows an embodiment wherein a shortened tail pipe 73 is usedwith the packer assembly 66 in the embodiment of FIGURE 9. The shortenedtail pipe is advantageous in using the gel mixture because it introducesthe gel-breaker into intimate contact with the mixture closely adjacentto the top whereby the floating particles can be readily washed free ofthe associated materials which might tend to retain them in the gel andprevent flotation. Use of the shorter tail pipe also facilitateshandling. Once the seal in the upper cavity 60 has been established byapplying pressure, the gel mixture is changed to the ordinary fracturingmixture that may include napalm, sand and crude oil. Continued pumpingof the fracturing fluid will cause a channel through the body offloating material 62 and te out through the fracturing cavity #0 intointimate and fracturing contact with theformation.

Example A Tar Spring Sandstone traversed by a five-inch LD. casing wastreated for fracturing, the fracture cavity being at 1347 :feet and thesealing cavity at 1353 feet, the latter two distances being measuredfrom the earths surface. The cutting tool was lowered into the well oncable tool apparatus. A sand and water mixture was employed for cutting,being delivered through a two-inch tubing at 17 barrels per minute and adischarge pressure of 3,000 lbs. per square inch. Operating under theseconditions, the sealing cavity was formed in fifteen minutes and thefracturing cavity was formed in thirty minutes. The plug was a mixtureof moth balls, sand, and a commercially available gelled acid. Theformation was fractured using 320 barrels of fracturing fluid deliveredat pressures in the range extending from 1650 to 1800 lbs. per squareinch. The fracturing il id was delivered over an eighteenminute periodof time. The composition of the fracttuing fluid was one pound of sandper gallon of salt water. The salt water was such as is found inassociation with petroleum minerals in the vicinity.

Swabbing at fifteen barrels per hour after fracturing lowered the fluidlevel steadily to the producing zone with increasing show of oil beingencountered in the swabbing fluid, thereby indicating successfulfracture of the oilbearing zone.

The foregoing example demonstrates an actual successful application ofthe subject method. The example also illustrates the feature of priorprophylactic action which produces the result of minimal loss offracturing fluid and 'fracturing fluid pressure in the treatment of theformation.

Under some present procedures for treating formations, it is known toshatter and/ or crack the cement surrounding the casing and to perforatethe casing at one or more points. The shattering of the cement is onsuch occasions desired in order that the fluid to be withdrawn from thesurrounding stratum is filtered by its passage through the shatteredcement, thereby removing sand and the like from Such fluid. The presentinvention further contemplates that the cement be suitably shattered andcracked, the casing perforated, and that a suitable washing action beapplied .by directing the abrading stream through the casingperforations against the cement in such a fashion as to wash away thecement While leaving some portions of the casing in place. In thisfashion, a suitable sealing cavity can be for-med throughout a 360 arcwhile portions of the casing are left in place. Alternatively, thecement can be removed by acidizing after being shattered. In such casethe acid has an inhibitor admixed therewith to protect the casing fromcorrosion las much as possible. The annular cavity can be formed in theformation after the acidizing has removed most of the cement.

In some instances it may not be essential that a bridge be emplacedprior to establis-hing the bed of plugging agent, eg. where operationsare near the bottom of the well.` In such instances the plugging agentis passed into the well until the bottom of the hole and the sealinUcavity are filled up.

In review it is seen that the invention includes a novel method ofdisposing a seal in such a fashion that channeling of treating fluids isconfined to the oil sand or desired producing formation. In addition,the force opposed to the channeling is proportional to that appliedbecause of the employment of treating pressure to seat the seal in theannulus or other cavity 38. Moreover, the seal can be readily emplacedprior to commencing the treating operation, whereby proble-ms of Waterdisplacement, loss of treating fluid and other problems attributable tothe channeling of the treating fluid along the casing-cement and/ or thecement-formation bond. The employment of abrasive cutting is preferredbecause sand can be used as the solid material.

the @braiding element. YThe suchcutting. Y

invention'isrnot'restricted to Y Whilefthe invention has been desc-ribedwithfrespect *Y to certain spe-cie apparatus, geological formations andthe like, it isto be understood that the Vstructures referred to are nolimitation uponthe-invention, and thatincluded within the invention areall the modications,substitu tions or equivalents, andthe like, whichwould be obvious.

having thisy disclosure ybefore him.

interiorV of the Ycasingand the formation; introducinginto' the casing abody of material including a liquid and particles ofless specic gravitythan the liquid; positioning a'removable casing plug above the body ofmaterial previously introduced, and moving the plug with the body ofmaterial ahead of it through, the casing to a position adjacent theupper one ofth'etwo zones at a'location 'such that the floatingparticles will extend fromV said plug down toa place intermediate thetwo zones; `and treating the formation by directing a liquid underpressure into a region common to the two zones whereby the pressure ofthe liquid urges the floating materials into the upperV of saidtwozonesfor sealingtenga-gement with the'jformation to seal against channelingof waterV and .treating liquid beyondthe sealing zone. t l

2.- A.method accordingto claim l wherein the step of positioning theplug includes providing a path for treatsteps of establishing.communication between theformation and the inside of the casingbyforming a lir'stvconjtmunicating cement-free zone between the formationand an internal portion of the casing, form'mg a second cornmunicatingcement-free zone above the'rst communicatingzone, introducing into thecasing .a body of liquid having floating thereupon a massof pluggingagenYand positioning the plugging agentfat a location within the casing thattraverses the second communicating zone, establishing a sealingmeanswithin the casing above the tioatingmass of material, andintroducing a treating tiuid.y

.under pressure intoj the casing ybeneath the plugging i l2 i v Ystructure to prevent channeling while pressure fluid treatment is made,comprising thesteps of removing a portion of the Acasing and' adjacentcement thereby establishing communication with said formation from theinside of vthe casing andthrough the cement rata preselected depthinlthe well adjacentV said formationthereby to form a fracturing cavity;establishing Vcommunication with said kformation from .the inside'of thecasing and through ythe cementfby completely removing van annular ringof the same at a second preselected depth in the wellV to form a sealingcavity in said formation, said second preselected depthrbeing greaterthan the tirst said preselected depth; plugging the casing below saidsealing cavity; introducing a bed of flowable particulate materialextending from thepoint of pluggingupwardly to a depth vintermediatesaid fracturing cavityand said sealing cavity, a portion of said bedbeing disposedwithin said sealingV cavity and fiowable intoconfining-relationship with` said lformation L responsive to pressure.applied thereto; .andv applying a Vfracturing fluid under pressure tosaid bed and through channeling, comprising -rthe steps of establishingcom- Y munication with saidiormation Afrom the inside of the casing andthrough thev cement at a preselected depth in the well'adjacent'saidformation by removing a portion `of the casing and adjacentrcemennmthereby to form a `treating cavity; establishing communicationwith saidl formation from the` inside of the casing by removing thesamev and through the cementV through an arc of 360r degrees Vatl asecondpreselectedl depth vin the well to form Van annular sealing cavityin said formation, 'said second preselected depth being greater than therst said preselected depth; `rplugging the lcasing below. said annularsealing cavity; introducing a bed of ilowable particulate i f materialextending VfrornltheV point of plugging'upwardly to` a depthintermediate' said treating cavity yand said annular sealing cavity, laportion of Isaid bed being disy under pressure to said vbed'and throughsaidffracturing cavity to said formation thereby to 4urge the lsaid bedinto confining relation with said formation in the region of saidannular Vsealing cavity and to treat said formation in the region ofsaid treating cavity whereby the seal acts agent and intofthe rstcommunicating Zone'and thence' under pressure into the formation fortreatment by the treating fluid, the floatingfmass of material beingurged by the pressure of the treating uidinto engagement with;

the sealingnneans and into-engagement with the formaltion adjacent thesecond communicating zone thereby p reventing the treating uid fromchanneling upward through the sealing means. v

4.A method inY accordance Withclaim Siwherein at least lonefof the stepsof .forming a communicating Zone includes the step of establishinga360annular cutextending through, the casing, the cement and into theformation; Y l' i 5,. A'method-in accordance with claimA 3, wherein thepluggingagent is taken from a groupconlsisting of iinely dividedexpanded cellular polystyrene, finely divided cellular polystyrene foam,finely divided cork, and tinely divided substantially solid materialtreated with a solventtoprevent` a channeling ,of the treating fluid.

8. A method of treating an'oil-bearing formation adjacent'acasingfand-cem'eut wellstructure to prevent channeling, comprisingthesteps of lestablishing communication with said'formation'ffrom,the.1inside of the casing vandvthrough,the-cement at a preselecteddepth in the (it).k

yvellbyre'moving angannular portion of said casing Vand adjacent cementto form a sealing cavity in said formai tion; thereafter establishingcommunication with said forresistantv material to reduce absorptionofthe liquid by A `method of treating an oil-bearing formation to,prevents channeling adjacent a casing-and-cement Well `mation from theinside' of the casing and through the -cement at.second preselecteddepth in the welladjacent saidfiformation by removing at least a portionof said vcasingand adjacent cement, thereby to Vform a treating icavity; said another. preselectedV depth being less .than

through said treating cavity to said formation thereby to urge theplugging agent in said bed into confining relation with said formationand to treat said formation in the region of said treating cavity, theplugging agent serving to prevent channeling through the sealing cavityand thence to water bearing formations.

9. A method of treating a producing formation adjacent acasing-and-cement well structure to prevent channeling, comprising the`steps of severing the cement at a preselected depth in the well,establishing communication between the inner portion of the casing andthe severed cement portion by removing a portion of the adjacent casing,thereby forming an annular sealing cavity; removing at least a portionof the casing and adjacent cement in the producing formation in spacedrelation with the annular sealing cavity; filling the annular sealingcavity with a plugging agent, treating the producing formation with auid, the plugging agent within the annular sealing cavity serving toprevent a migration of the treating fluid into areas beyond the sealingcavity by channeling into water producing formations through a rupturein the cement-formation bond.

10. A method of treating a producing formation adjacent acasing-and-cement well structure to prevent channeling during pressurefluid treatment into adjacent water bearing formations, comprising thesteps of establishing communication with said formation from the insideof the casing through the cement at at least two preselected depths inthe well adjacent said formation by removing a portion of the casing andall of the adjacent cement, thereby to form a treating cavity and asealing cavity; introducing a bed of plugging agent to till said sealingcavity, a portion of said bed being disposed within said sealing cavityand tiowable into confining relationship with said formation responsiveto pressure applied thereto; introducing a treating fluid adjacent thetreating cavity; and applying a pressure to said bed and treating fluidthrough said fracturing cavity to said formation thereby to urge theplugging agent in said sealing cavity into confining relation with saidformation in the region of said sealing cavity to prevent the channelingof pressure uids into adjacent water bearing formations.

11. A method according to claim 10 wherein both said cavities areconcurrently established.

12. A method according to claim 10 wherein said step of establishingcommunication forms said treating cavity first.

13. A method according to claim 10 wherein said step of establishingcommunication forms said sealing cavity first.

14. A method according to claim 10 wherein said step of establishingcommunication forms said sealing cavity as an annulus extending throughan arc of 360 degrees.

l5. A method according to claim 10 wherein said step of establishingcommunication forms said sealing cavity as an annulus extending throughan are of 360 degrees and said plugging agent comprises sand.

16. A method according to claim 10 wherein said step of establishing abed comprises flowing aparticulate material into the sealing cavity.

17. A method according to claim 10 wherein said step of establishingcommunication includes flowing a liquid stream containing abradingparticles into abrading and eroding contact with said casing, cement,and formation.

18. A method of treating a geological formation adjacent acasing-and-cement Well structure, comprising the steps forming a zone ofentrance into the formation, forming a sealing cavity above theformation, positioning a sealing means above and adjacent to the sealingcavity, introducing a floating plugging agent into the casing in aquantity calculated to fill the space below the sealing means andcovering the sealing cavity, treating the formation with a pressure uid,the pressure of the fluid serving to lill the sealing cavity with theiioating plugging agent While the formation is being treated, theplugging agent thereby blocking any channeling of the treating fluidthrough the sealing cavity.

References Cited in the tile of this patent UNlTED STATES PATENTS2,368,424 Reistle an. 30, 1945 2,805,721 Maly Sept. 10, 1957 2,842,205Allen July 8, 1958 2,970,645 Glass Feb. 7, 1961

9. A METHOD OF TREATING A PRODUCING FORMATION ADJACENT ACASING-AND-CEMENT WELL STRUCTURE TO PREVENT CHANNELING, COMPRISING THESTEPS OF SEVERING THE CEMENT AT A PRESELECTED DEPTH IN THE WELL,ESTABLISING COMMUNICATION BETWEEN THE INNER PORTION OF THE CASING ANDTHE SEVERED CEMENT PORTION BY REMOVING A PORTION OF THE ADJACENT CASING,THEREBY FORMING AN ANNULAR SEALING CAVITY; REMOVING AT LEAST A PORTIONOF THE CASING AND ADJACENT CEMENT IN THE PRODUCING FORMATION IN SPACEDRELATION WITH THE ANNULAR SEALING CAVITY; FILLING THE ANNULAR SEALINGCAVITY WITH A PLUGGING AGENT, TREATING THE PRODUCING FORMATION WITH AFLUID, THE PLUGGING AGENT WITHIN THE ANNULAR